In engines, a valve-driving mechanism is provided in order to actuate intake and exhaust valves for opening and closing air inlet and outlet ports of a combustion chamber. FIGS. 7 and 8 illustrate such a valve-driving mechanism. In this mechanism, each rocker arm 102 is defined with a-rocker shaft hole 104 through which a rocker shaft 106 is inserted. The rocker arm 102 includes a cam-side abutting portion 108 which is positioned in contact with a cam 112 mounted on a camshaft 110. The rocker shaft 106 has an oil passage 114 formed on a shaft axis C. The rocker shaft 106 is further formed with an oil flow communication aperture 116 which is radially oriented to communicate with the oil passage 114.
The rocker arm 102 further includes a valve-side pressing portion 118 which is provided with a hydraulic adjuster (H. L. A.) 120. The hydraulic adjuster 120 contacts a valve stem end 124 of an air intake and exhaust valve 122.
In addition, to introduce oil into the hydraulic adjuster 120, an adjuster-side oil aperture 126 and an adjuster-side oil passage 128 are formed in the rocker shaft 106 and the rocker arm 102, respectively.
The rocker arm 102 is pivotably supported on the rocker shaft 106. The axial position of the rocker arm 102 is determined by a head thrust surface 132 of a cylinder head 130. The rocker shaft 106 has a spiral spring 134 in engagement therewith, which spring causes the rocker arm 102 to be pressed against the head thrust surface 132. A sliding or bearing portion between the rocker arm 102 and the rocker shaft 106 is subjected to lubrication through the supply of oil thereto from the oil passage 114 and the oil flow communication aperture 116.
When the rocker shaft spring 134 is set at a greater load, friction exerted on the rocker arm 102 in a thrust direction increases. Accordingly, the spring 134 is set at a load which is minimized to a level required to hold the rocker arm 102 in position.
One example of the aforesaid rocker arm is disclosed in, for example, published Japanese Utility Model Application Laid-Open No. 3-6008. In the rocker arm of this publication, a bearing portion is located midway along a swingable arm portion of the rocker arm. The swingable arm portion is provided with a pressing portion at one end and a contact portion at the other end. The pressing portion serves to press a valve stem of a valve body, and is curved in a desired direction. The contact portion contacts a camshaft. The bearing portion is provided with a protruding portion. The protruding portion extends in a stepped manner toward a curvilinear region of the pressing portion so as to provide a maximum protrusion at a lower end region of the bearing portion. Further, the protruding portion includes a staged portion at a lower end, inner peripheral region of the bearing portion.
In a rocker arm as shown in FIGS. 7 and 8, flow of oil, which is supplied through the oil flow communication aperture 116, is directed between the rocker arm 102 and the head thrust surface 132 on the cylinder head 130. The resulting hydraulic pressure causes the rocker arm 102 to be lifted off the head thrust surface 132, and as a result the rocker arm 102 is moved away from the head thrust surface 132. This causes inconveniences in that the stem end 124 of valve 122 and hydraulic adjuster 120 assume out-of-line positions, whereby the valve stem end 124 pitches or an unusual sound is emitted. There is a further inconvenience in that the hydraulic adjuster 120 is disengaged from the valve stem end 124 when the rocker arm 102 is forced to move a large distance.
To obviate the above-described inconveniences, a first aspect of the present invention provides a rocker arm defined with a rocker shaft hole, through which a rocker shaft is inserted, the rocker shaft having an oil passage defined on a shaft axis, the rocker shaft being further formed with an oil flow communication aperture which is radially directed to communicate with the oil passage, the axial position of the rocker arm being determined by a head thrust surface of a cylinder head, comprising the improvement wherein an arm thrust surface of the rocker arm is provided with an oil groove having a predetermined depth, the arm thrust surface being in abutment with the head thrust surface of the cylinder head, the oil groove communicating with the rocker shaft hole so as to introduce oil outside.
A second aspect of the present invention provides a rocker arm defined with a rocker shaft hole, through which a rocker shaft is inserted, the rocker shaft having an oil passage defined on a shaft axis, the rocker shaft being further formed with an oil flow communication aperture which is radially directed to communicate with the oil passage, the axial position of the rocker arm being determined by a head thrust surface of a cylinder head, comprising the improvement wherein an arm thrust surface of the rocker arm is provided with an oil groove having a predetermined depth, the arm thrust surface being in abutment with the head thrust surface of the cylinder head, the oil groove communicating with the rocker shaft hole so as to introduce oil outside, and wherein the arm thrust surface further has a chamfered portion provided around the rocker shaft hole, the chamfered portion being greater in depth than the oil groove.
According to the construction of the present invention, when oil overflows from a location at which a rocker arm is positioned in scraping contact with an oil flow communication aperture and a rocker shaft, the oil is blocked from penetrating between an arm thrust surface of the rocker arm and a head thrust surface of a cylinder head, but is guided into an oil groove so as to be discharged outside. The rocker arm is thereby prevented from being dislodged and isolated from the head thrust surface. This feature can prevent the occurrence of pitching of the valve stem end and vibration or noise from the valve-driving system.
Furthermore, since the rocker arm is held in engagement with the head thrust surface, the rocker shaft spring can be set at a lighter load. As a result, low friction is achievable.